The invention relates to an improved process for converting hydrocarbons, preferably non-aromatic hydrocarbons, in the presence of an improved zeolite material, to aromatic hydrocarbons and lower olefin hydrocarbons preferably with a low rate of coke formation during the conversion of such hydrocarbons in the presence of such improved zeolite material.
It is known to catalytically crack gasoline boiling range hydrocarbons (in particular, non-aromatic gasoline boiling range hydrocarbons, more in particular, paraffins and olefins) to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene, and xylene, and also ethylbenzene) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N. Y. Chen et al. in Industrial & Engineering Chemistry Process Design and Development, Volume 25, 1986, pages 151-155. The reaction product of this catalytic cracking process contains a multitude of hydrocarbons such as unconverted C.sub.5 + alkanes, lower alkanes (methane, ethane, propane), lower alkenes (ethylene and propylene), C.sub.6 -C.sub.8 aromatic hydrocarbons (e.g., benzene, toluene, xylene, and ethylbenzene), and C.sub.9 + aromatic hydrocarbons. Depending upon the relative market prices of the individual reaction products, it can be desirable to increase the yield of certain of the more valuable products relative to the others.
One concern with the use of zeolite catalysts in the conversion of hydrocarbons to aromatic hydrocarbons and lower olefins is the excessive production of coke during the conversion reaction. The term "coke" refers to a semi-pure carbon generally deposited on the metal surfaces of process equipment or a catalyst. Coke formed during the zeolite catalyzed aromatization of hydrocarbons tends to cause catalyst deactivation. It is desirable to improve processes for the aromatization of hydrocarbons, and the formation of lower olefins from hydrocarbons, by minimizing the amount of coke formed during such processes. It is also desirable to have a zeolite catalyst that is useful in producing significant quantities of the aromatic and olefin conversion products.